1. Technical Field of the Invention
The present invention relates generally to electrically powered ceramic composite heaters for devices such as an electrical smoking article and more particularly to a tubular ceramic heater for use in an electrical smoking article.
2. Discussion of the Related Art
Previously known conventional smoking devices deliver flavor and aroma to the user as a result of combustion of tobacco. A mass of combustible material, primarily tobacco, is oxidized as the result of applied heat with typical combustion temperatures in a conventional cigarette being in excess of 800.degree. C. during puffing. Heat is drawn through an adjacent mass of tobacco by drawing on the mouth end. During this heating, inefficient oxidation of the combustible material takes place and yields various distillation and pyrolysis products. As these products are drawn through the body of the smoking device toward the mouth of the user, they cool and condense to form an aerosol or vapor which gives the consumer the flavor and aroma associated with smoking.
Conventional cigarettes must be fully consumed or be discarded once lit. A prior alternative to the more conventional cigarettes include those in which the combustible material itself does not directly provide the flavorants to the aerosol inhaled by the smoker. In these smoking articles, a combustible heating element, typically carbonaceous in nature, is combusted to heat air as it is drawn over the heating element and through a zone which contains heat-activated elements that release a flavored aerosol. While this type of smoking device produces little or no sidestream smoke, it still generates products of combustion, and once lit it is not adapted to be snuffed for future use in the conventional sense.
In both the more conventional and carbon element heated smoking devices described above combustion takes place during their use. This process naturally gives rise to many by-products as the combusted material breaks down and interacts with the surrounding atmosphere.
Commonly assigned U.S. Pat. Nos. 5,093,894; 5,224,498; 5,060,671 and 5,095,921 disclose various electrical resistive heating elements and flavor generating articles which significantly reduce sidestream smoke while permitting the smoker to selectively suspend and reinitiate smoking. However, the cigarette articles disclosed in these patents are not very durable and may collapse, tear or break from extended or heavy handling. In certain circumstances, these prior cigarette articles may crush as they are inserted into the electric lighters. Once they are smoked, they are even weaker and may tear or break as they are removed from the lighter.
U.S. patent application Ser. No. 08/118,665, filed Sep. 10, 1993, describes an electrical smoking system including a novel electrically powered lighter and novel cigarette that is adapted to cooperate with the lighter. The preferred embodiment of the lighter includes a plurality of metallic sinusoidal heaters disposed in a configuration that slidingly receives a tobacco rod portion of the cigarette.
The preferred embodiment of the cigarette of Ser. No. 08/118,665 preferably comprises a tobacco-laden tubular carrier, cigarette paper overwrapped about the tubular carrier, an arrangement of flow-through filter plugs at a mouthpiece end of the carrier and a filter plug at the opposite (distal) end of the carrier, which preferably limits air flow axially through the cigarette. The cigarette and the lighter are configured such that when the cigarette is inserted into the lighter and as individual heaters are activated for each puff, localized charting occurs at spots about the cigarette. Once all the heaters have been activated, these charred spots are closely spaced from one another and encircle a central portion of the carrier portion of the cigarette. Depending on the maximum temperatures and total energies delivered at the heaters, the charred spots manifest more than mere discolorations of the cigarette paper. In most applications, the charring will create at least minute breaks in the cigarette paper and the underlying carrier material, which breaks tend to mechanically weaken the cigarette. For the cigarette to be withdrawn from the lighter, the charred spots must be at least partially slid past the heaters. In aggravated circumstances, such as when the cigarette is wet or twisted, the cigarette may be prone to break or leave pieces upon its withdrawal from the lighter. Pieces left in the lighter fixture can interfere with the proper operation of the lighter and/or deliver an off-taste to the smoke of the next cigarette. If the cigarette breaks in two while being withdrawn, the smoker may be faced not only with the frustration of failed cigarette product, but also with the prospect of clearing debris from a clogged lighter before he or she can enjoy another cigarette.
The preferred embodiment of the cigarette of Ser. No. 08/118,665 is essentially a hollow tube between the filter plugs at the mouthpiece end of the cigarette and the plug at the distal end. This construction is believed to elevate delivery to the smoker by providing sufficient space into which aerosol can evolve off the carrier with minimal impingement and condensation of the aerosol on any nearby surfaces. Ser. No. 08/118,665 also discloses an electrical smoking article having heaters which are actuated upon sensing of a draw by control and logic circuitry.
Although these devices and heaters overcome the observed problems and achieve the stated objectives, many embodiments are plagued by the formation of a significant amount of condensation formed as the tobacco flavor medium is heated to form vapors. These vapors can cause problems as they condense on relatively cooler various electrical contacts and the associated control and logic circuitry. The condensation can cause shorting and other undesired malfunctions. In addition, condensation can influence the subjective flavor of the tobacco medium of the cigarette. Though not desiring to be bound by theory, it is believed that the condensation is the result of the flow pattern and pressure gradient of ambient air drawn through the article and the current designs of the heater assemblies. The proposed heaters are also subject to mechanical weakening and possible failure due to stresses induced by inserting and removing the cylindrical tobacco medium. In addition, the electrical smoking articles employ electrically resistive heaters which have necessitated relatively complex electrical connections which could be disturbed by insertion and removal of the cigarette.
U.S. Pat. Nos. 5,060,671 and 5,093,894 disclose a number of possible heater configurations, many of which are made from a carbon or carbon composite material formed into a desired shape. In several of the disclosed configurations, the heater includes a plurality of discrete electrically resistive heating segments that can be individually activated to provide a single puff of flavor to the user. For example, one configuration involves a radial array of blades connected in common at the center and separately connectable at their outer edges to a source of electrical power. By depositing flavor-generating material on each blade and heating the blades individually, one can provide a predetermined number of discrete puffs to the user. Other configurations include various other arrays of discrete fingers or blades of heater material, or various linear and tubular shapes subdivided to provide a number of discrete heating areas. Such configurations of discrete heating segments may allow for more efficient consumption of power and more efficient use of heater and flavor-generating material.
It has proven difficult, however, to arrange suitable heater materials in the above-described configurations. A suitable heater material must exhibit, among other things, a resistivity sufficient to allow for rapid heating to operating temperatures. It is also desirable that the heater resistance correspond to the energy density of the power source in order to minimize power consumption. Suitable heater materials of low mass, such as those described in the above-incorporated patents, must generally also be of very low density, however, and thus are difficult to arrange in such discrete heater segment configurations. Such low density characteristics complicate, or make impossible, assembly of the configurations by simple, well-known manufacturing techniques. Even after successful manufacture, such configurations are often unacceptably fragile for use within a flavor-generating article. These problems can be overcome to some extent with the aid of highly sophisticated manufacturing techniques. However, in manufacturing the heaters which are disposable and replaceable, these techniques become prohibitively expensive.
It would thus be desirable to provide a discrete heater configuration of suitable heater material that is sufficiently strong for use within a flavor-generating article without threat of breakage during manufacture. It would also be desirable to be able to manufacture such a heater with a discrete heater segment configuration using well-known, inexpensive manufacturing techniques.
Various ceramic heating compositions are described in U.S. Pat. Nos. 5,045,237 and 5,085,804. Also, British Patent No. 1,298,808 and U.S. Pat. Nos. 2,406,275; 3,875,476; 3,895,219; 4,098,725; 4,110,260; 4,327,186; and 4,555,358 relate to electrically conductive ceramic heater materials.